User blog:Samuli.seppanen/The handle and cheiroballistra pullback
EDIT: This blog post became a real article. The current incarnation of my cheiroballistra handle is a simplification of the Iriarte-style handle. When not attached to the slider, the handle look like this: It's attached to slider like this: It is locked to a strong pin attached to the case, and is partially auto-locking: "Partially auto-locking" means that a small tap with a palm is required to really lock it. Further information about the handle is available on these pages: * Making round cheiroballistra handle * Attaching the handle to the slider * User blog:Samuli.seppanen/Fixes, bugs and performance improvements (blog post) In my reconstruction the handle is attached as close to the claw and trigger as possible - not to the very end of the slider as suggested by the cheiroballistra manuscript. The reason for this design choice is that having the axle at the end of the slider is just stupid: the wood will split at the axle when the handle is locked to the pin and stomach pressure is released. While circumventing the problem with metal reinforcements is certainly doable, why fix an inherently broken design when there is plenty of space at the end of the slider for moving the handle's axle forward? In a nutshell there is a good reason why the handle axle should be where I put it, and no good reason why it should be at the end of the slider. So, in this case, I rather trust common sense than the manuscript, as they're clearly contradicting each other. One can of course question whether the handle was used for locking the slider to the case, but then again, the only other reasonable option, the pitarion, seems far less likely candidate. I don't want to start inventing "missing parts", either, because so far I've had no need for any, and the cheiroballistra is already shooting faster than any other scholarly reconstructions out there that I'm aware of (Nick's Firefly is of course still clearly ahead when it comes to velocity, but that's fine; I'm content if I get 100 m/s or 328 fps coupled with reasonable efficiency levels). Now, is my current interpretation of the handle the correct one or not? While the current handle certainly works beautifully, there are issues not directly related to the handle itself, but the potential energy storage of the cheiroballistra. Cheiroballistra's closest analogy, the stomach-cocked gastraphetes, which used a normal bow as it's power source, had ratchets and pawls which served as a way to automatically lock the slider at certain intervals. Heron is somewhat unclear regarding how the gastraphetes was cocked: After that they rested the end of the slider, that had been pushed out, against a wall or the ground and, holding in their hands the ends of the withdrawal-rest ΤΥΦΧΨ, they pressed the belly against the concavity ΧΨ. Straining hard with the whole body, they pushed the slider back and drew back the bowstring... (translation from Marsden 1971: 23) If the above translation is more or less correct, it would seem that both stomach pressure (push) and hands (pull) we used to cock the weapon. This makes perfect sense, as it allows use of a much stronger bow with no real downside. According to Marsden (1971: 46) Diels & Schramm (1918) describes the cocking process well. Unfortunately I don't have this research paper yet, so I can't check what the exact interpretation was. Regardless I think it is fairly safe to assume that hands were used to assist cheiroballistra's draw. Stomach pressure alone might - based on my current experience - yield ~100 joules of projectile energy at most for a 90 kilo person. Assisting the drawback with hands might add maybe 50 joules, depending on the technique. That said, if I ever get 150 joule levels with the cheiroballistra I will be extremely happy. So, how could we assist the drawback with both hands? Simply pulling the bowstring is out of the question because at the end of the draw, where assistance is needed the most (due to the peak in the force-draw curve), the bowstring angle is too acute. So we really only have two viable options: # Use hands to pull back the arms # Use hands to pull back the slider The first option is certainly doable, but the length of hand movement is fairly limited and any performance improvement would probably be fairly modest. Care would also have to be taken to pull each arm equally, so that one arm is not rotated more than the other. This problem is essentially the same as with bows and crossbows - if otherwise perfectly balanced limbs are pulled unevenly, one limb will be strained more and will move quicker when the bowstring is released, resulting in erratic sideways movement of the bolt's butt-end. Due to a combination of high pressure and friction between the nut or the claw and (acute) bowstring angle the limbs or arms are unable to correct their position without assistance. Additionally this way of assisting the pullback would require the handle (χειρολάβη) to be able to automatically lock to the pin in the case, and P.H. does not describe any springs or anything similar that could serve that purpose. Unless, of course, we assume the pitarion (πιττάριον) is some sort of spring, which is of course possible, but not very likely in my opinion. The second option - pulling back the slider with both hands - seems a lot more likely. However, what part of the slider construction would one pull? This brings us back to the χειρολάβη, which translates literally to "something grasped with hand(s)", or "handle". For some reason other scholars have not been keen to interpret the "handle" as as a handle. The primary reason is probably the size of the handle in the manuscript diagrams, where the handle is shown narrower than the top of the slider. As the proportions in most of the cheiroballistra manuscripts diagrams are generally way off, I don't see why we should think they're more of less correct when it comes to the triggering mechanism. In fact, when we disregard the proportions, the handle looks a lot like, well, a handle. Also, why would a part called the handle not be used as such, especially if it would actually serve two very useful purposes: * Increase energy storage considerably * Allow easy manual locking of the slider to the pin(s) and thus the case, doing away with the need for auto-locking mechanisms I will definitely make a simple T-shaped pullback handle the next time I visit the forge and see how it works in practice. I'm fairly close to reaching the maximum power levels obtainable with stomach pressure alone, so I need to do something to squeeze more power out of the thing. Category:Blog posts Category:Backup Category:Cheiroballistra Category:Lock Category:Theoretical Category:Gastraphetes Category:Cocking devices